The invention relates to a cylinder head for an internal combustion engine, comprising at least one first cooling chamber on the fire deck side and one second cooling chamber which adjoins the first cooling chamber in the axial direction of the cylinder, wherein the lower and upper cooling chamber are separated from each other by means of an intermediate deck, wherein a central receptacle is arranged for an injection nozzle or ignition device for each cylinder, and wherein the first and the second cooling chambers are flow-connected to each other in the region of the central receptacle, and comprising at least two, preferably four, gas exchange valves per cylinder, wherein the first cooling chamber comprises a radial cooling duct in the region of at least one valve bridge between two gas exchange valves.
The flow balance between the valve bridges occurs in two-part water jackets nearly exclusively by forming the radial expansion of the associated intermediate deck passages. As a result of the higher need for cooling in the exhaust valve bridge, the radial expansion is greatest at this location. This however impairs the vertical flow pulse and the approach of the flow to the injection nozzle. Since the main influencing factor of the LCF security (low cycle fatigue) on the thermal expansion along the entire valve bridge (from the injector up to the outer contour of the cylinder head) is relevant, cooling shall be provided positively over the largest possible area and shall not only be aimed at the narrow ranges of the peak temperature. As a result of the expanding cross-sections in the cooling chamber from the injection nozzle to the outer contour, the flow velocity decreases continuously and turbulence effects from the narrow gaps subside. Furthermore, stagnation points form on the circumference of the valve seats by the deflection of the flow towards the main outlets in these outer cylinder head regions. As a result of the HCF loading (high cycle fatigue), greater fire deck strengths are required in the outer regions of the valve bridges, so that the locally lower gas-side heat inputs already lead to very high structural temperatures in the range of the permissible material limit values.
It is a general object of the flow guidance to provide the adjustment of the local coefficients of speed transition and heat transfer according to the local heat inputs and the structural temperatures.
DE 10 339 244 A1 discloses a cylinder head with a first and a second cooling chamber, wherein the two partial cooling chambers are flow-connected to each other in the region of a central receptacle for an injector or a spark plug. The lower and the upper partial cooling chamber are separated from each other by an intermediate deck. Cooling ducts are arranged in the region of the valve bridges between two adjacent inlet and exhaust valves, wherein the intermediate deck comprises a lowered portion in the region of the central receptacle. The lowered portion decreases the first cooling chamber in the inner region, which has a disadvantageous effect however on the cooling of the thermally critical central regions of the fire deck.
U.S. Pat. No. 4,567,859 A shows a cylinder head for an internal combustion engine with a cooling chamber extending over several cylinders in the longitudinal direction, wherein the ceiling of the cooling chamber facing the fire deck comprises a respective suspended rib in the region of transverse planes between two adjacent cylinders. A similar configuration is also known from JP 56-148 647 A or JP 61-149 551 A.
It is the object of the invention to prevent stagnation zones in the outer region of the first cooling chamber and to improve the heat dissipation from LCF-critical zones in the outer region of the valve bridges and the valve centre.